This invention relates to an ultrasonic linear motor using an electromechanical energy converting element as a driving source, such as an ultrasonic linear motor that moves a driven member linearly by means of a standing-wave ultrasonic motor.
In recent years, an increasing number of ultrasonic motors have been used in the fields of precision machines and optical instruments, because ultrasonic motors have the advantage of being smaller in size, producing a higher torque, having a longer stroke, and providing a higher resolution than electromagnetic motors. Such ultrasonic motors are roughly divided into the rotary type and the linear type. Ultrasonic motors of the linear type have been disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-284752 and U.S. Pat. No. 5,416,375.
To the ultrasonic motor disclosed in Jpn. Pat. Appln. KOKAI Publication No. 6-284752, an electromechanical energy converting element is stuck. The longitudinal dimension and breadthwise dimension of the ultrasonic motor are set so that the resonance frequency at which the electromechanical energy converting element expands and contracts longitudinally may coincide with the frequency at which a traverse elastic wave whose propagation direction is the direction in which the converting element expands and contracts should stand.
Furthermore, the ultrasonic motor is provided with a vibrator on which an expanding and contracting vibration and a standing wave are generated simultaneously according to the vibrational displacement of the electromechanical energy converting element and with sliding projections that are provided so as to project from the position corresponding to bellies of the standing wave on the surface of the vibrator and are driven by the vibration of the vibrator so as to draw a rotary locus. Additionally, the ultrasonic motor is provided with a support shaft so that it may project from both side faces of the vibrator at the position corresponding to a node of the standing wave on the vibrator. When the support shaft is pressed downward, the vibrator is pressed against the driven member, causing the driven member to be moved according to the vibration of the vibrator.
FIGS. 9A and 9B schematically show the configuration of an example of the above-mentioned ultrasonic liner motor. FIG. 9A is a plan view and FIG. 9B is a front sectional view. As shown in FIGS. 9A and 9B, the vibrator 2 is composed of an elastic material 3 taking the form of an almost rectangular parallelopiped. At the top of the elastic material 3, two rectangular cutouts 3a are made in the lengthwise direction. Into each of the cutouts 3a, a laminated piezoelectric element 4 is fitted and fixed. In the two positions on the bottom surface of the elastic material 3 at which bellies of the vibration appear, sliding members 5 are stuck with a one-to-one correspondence. The vibrator 2 is provided with a support shaft 6 so that the shaft may project from both sides of the elastic member 3 at the position that corresponds to a node of the second-order standing wave and is between the two laminated piezoelectric elements 4.
The vibrator 2 is supported, via the support shaft 6 acting as a force acting point, by a hook member 7 with a recessed section that engages with the support shaft 6, and is pressed toward a driven member 9 via the sliding members 5. The hook member 7 is fastened to one end of a cantilever plate spring 11 with a screw 121. The other end of the plate spring 11 is secured to a base 14 via a pedestal 13 with a screw 122. In Jpn. Pat. Appln. KOKAI Publication No. 6-284752, in addition to the aforementioned configuration, a configuration where the way of installing the plate spring and the shape of the plate spring have been improved, has also been disclosed as means for exerting force on the vibrator 2.
The aforementioned ultrasonic linear motor has the advantage of having a high resolution and a long stroke. To make use of these advantages, the ultrasonic linear motor is provided with a linear guide that moves the driven member accurately. In the conventional example, however, the related construction between the base 14 to which the plate spring 11 is secured and the driven member 9 has not been disclosed clearly and therefore it cannot be said definitely that the ultrasonic linear motor has a compact, high-performance structure. It is known that in the ultrasonic linear motor, a change in the force pressing the vibrator 2 results in a change in the driving thrust. Thus, the force pressing the vibrator 2 has a great effect on the characteristics of the motor.
The aforementioned ultrasonic linear motor, however, has a disadvantage in that since the pressing force is determined by the plate spring 11 used, errors in producing the remaining component parts including the plate spring 7 lead to a change in the pressing force, having an effect on the characteristics of the motor. In the case of a compact ultrasonic linear motor, in particular, the span of the plate spring 11 cannot be made too long, and inevitably a plate spring with a large spring constant is used, making the motor more liable to be affected by the aforesaid errors in production. There is another problem: because the plate springs 11, 11 press the support shaft 6 on both sides of the vibrator 2 separately, a difference in force between the two plate springs 11, 11 occurs, which prevents the vibrator 2 from being pressed perpendicularly against the driven member 19, making the movement of the driven member 9 unstable.
On the other hand, U.S. Pat. No. 5,416,375 has disclosed an ultrasonic linear motor where a coil spring is used to press the vibrator against the driven member and the pressing force of the coil spring is adjustable with an adjusting screw. In such an ultrasonic linear motor, the frame supporting the coil spring is larger than the miniaturized vibrator. The support member supports the vibrator so as to prevent the vibrator from being moved in the direction in which the driven member moves, while the vibrator is being pressed by the coil spring. A construction for supporting the vibrator, however, has not been disclosed clearly in the publication. If a concrete support mechanism is used, the configuration will become larger, causing a problem: the dimensions of the entire ultrasonic linear motor will be larger and production cost will rise.
As described above, the conventional ultrasonic linear motors have the problem that although the vibrator has been miniaturized, means for supporting and pressing the vibrator has not been miniaturized, resulting in a larger configuration and in the difficulty of producing a stable pressing force to the vibrator.